ynl: support binary and integer sub-type for indexed-array

Add binary and integer sub-type support for indexed-array to display bond
arp and ns targets. Here is what the result looks like:

 # ip link add bond0 type bond mode 1 \
   arp_ip_target 192.168.1.1,192.168.1.2 ns_ip6_target 2001::1,2001::2
 # ./tools/net/ynl/cli.py --spec Documentation/netlink/specs/rt_link.yaml \
   --do getlink --json '{"ifname": "bond0"}' --output-json | jq '.linkinfo'

    "arp-ip-target": [
      "192.168.1.1",
      "192.168.1.2"
    ],
    [...]
    "ns-ip6-target": [
      "2001::1",
      "2001::2"
    ],

Signed-off-by: Hangbin Liu <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: liuhangbin

Documentation/userspace-api/netlink/genetlink-legacy.rst

@@ -66,9 +66,13 @@ looks like::
       [MEMBER1]
       [MEMBER2]
 
-It wraps the entire array in an extra attribute (hence limiting its size
-to 64kB). The ``ENTRY`` nests are special and have the index of the entry
-as their type instead of normal attribute type.
+Other ``sub-type`` like ``u32`` means there is only one member as described
+in ``sub-type`` in the ``ENTRY``. The structure looks like::
+
+  [SOME-OTHER-ATTR]
+  [ARRAY-ATTR]
+    [ENTRY u32]
+    [ENTRY u32]
 
 type-value
 ~~~~~~~~~~

tools/net/ynl/lib/ynl.py

@@ -641,6 +641,16 @@ def _decode_array_attr(self, attr, attr_spec):
             if attr_spec["sub-type"] == 'nest':
                 subattrs = self._decode(NlAttrs(item.raw), attr_spec['nested-attributes'])
                 decoded.append({ item.type: subattrs })
+            elif attr_spec["sub-type"] == 'binary':
+                subattrs = item.as_bin()
+                if attr_spec.display_hint:
+                    subattrs = self._formatted_string(subattrs, attr_spec.display_hint)
+                decoded.append(subattrs)
+            elif attr_spec["sub-type"] in NlAttr.type_formats:
+                subattrs = item.as_scalar(attr_spec['sub-type'], attr_spec.byte_order)
+                if attr_spec.display_hint:
+                    subattrs = self._formatted_string(subattrs, attr_spec.display_hint)
+                decoded.append(subattrs)
             else:
                 raise Exception(f'Unknown {attr_spec["sub-type"]} with name {attr_spec["name"]}')
         return decoded